Cold cathode gas discharge tubes



y 11, 1965 N. D. CRAKER |=:rA|. 3,183,392

cow CATHODE GAS DISCHARGE TUBES Filed Dec. 4, 1961 2 Sheets-Sheet 2 mg 9. Fig .10.

ATTORNEY United States Patent 3,183,392 COLD CATHQDE GAS DESCHARGE TUBES Noel David Craker and George Peter Stemming, Stanmore, Middlesex, and Frank Temple Cotton, Chalfont St. Giles, England, assignors to Hivac Limited, South Ruislip, England, a British company Filed Dec. 4, 1961, Ser. No. 156,571 Claims priority, application Great Britain, Dec. 8, 1960, 42,305/60 Claims. (Cl. 313188) This invention relates to cold cathode gas discharge tubes and is more particularly concerned with tubes of the so-called trigger type in which breakdown of the main discharge path between cathode and anode is initiated by a triggering discharge brought about by application of a suitable control potential to a further or trigger electrode.

In co-pending application Serial No. 156,570, filed Dec. 4, 1961, by George Peter Stenning, there is described an improved trigger tube construction in which the cathode is a small size element located in and surrounded by an enclosing or confining anode and in which the trigger electrode is also arranged to surround or substantially surround the cathode at a position between the cathode and the anode. With such a formation, practical constructional difliculties may arise in setting the dimension of the trigger gap between the trigger electrode and the cathode at its suitable and very small value and at a proper position where it is fully effective to initiate the main discharge between cathode and anode. If, for any reason, the minimum spacing distance between any part of the trigger electrode and the cathode should prove to be at a position which is obscured from the view of the anode, for instance, at a location deep within a cylindrical trigger electrode instead of at its open end and hence not readily visible by the anode, there is a risk that reliable triggering will not be obtained and the operation of the tube accordingly rendered erratic and defective.

One object of the present invention is to provide an improved tube construction by which such difliculty may be avoided while another object is the provision of a tube construction in which the de-ionisation time is reduced to a low value. The invention, while the particular application to tube constructions as described in the aforesaid co-pending application, has wider application to trigger-type discharge tubes generally and is useful with tube arrangements of the more conventional form in which the cathode is the outermost element and co-operates with a central anode.

According to the broadest aspect of the invention, the trigger electrode is formed as a member of foraminated metal sheet, wire mesh, grid or like apertured character which is so placed between the cathode and anode electrodes of the tube that the whole or substantially the whole of the main discharge passes through the openings therein. Preferably, such trigger electrode is arranged to surround and effectively enclose one of the said cathode or anode electrodes. By reason of the apertured character of the trigger electrode, the ionisation produced by the triggering discharge between the trigger electrode and the co-operating main electrode, wherever it may occur, is always available to the main discharge zone between the two main electrodes and in consequence the main discharge is readily initiated. In addition, it has been found that, by reason of the apertured character of the trigger electrode, the main discharge in passing therethrough is eflfectively split up into a number of discrete columns or layers and in this way every part of the dis: charge necessarily passes close to a portion of the trigger electrode and this, in turn, is conducive to shorter recovery or de-ionisation time upon cessation of the discharge.

3,183,392 Patented May 11, 1965 ice In order that the nature of the invention may be more readily understood, a number of constructional embodiments thereof will now be described by way of illustrative example only and with reference to the accompanying drawings in which:

FIG. 1 is a schematic axial sectional view of one form of discharge tube constructed in accordance with the invention;

FIG. 2 is a schematic end view of the tube construction shown in FIG. 1;

PEG. 3 is an axial sectional view similar to FIG. 1 of a modified form of tube;

FIG. 4 is a schematic axial sectional view of an alternative form of electrode structure;

FIGS. 5 and 6 are axial sectional and plan views respectively of a further embodiment of the invention;

FIGS. 7 and 8 are axial sectional and plan views respectively of yet a further electrode arrangement according to the invention;

FIG. 9 is an axial sectional view of a further modification;

FIGS. 10 and 11 are axial sectional and plan views respectively of a further embodiment;

FIGS. 12 and 13 are perspective views of alternative forms of trigger electrode construction; while FIGS. 14 and 15 are axial sectional and plan views respectively of yet another arrangement according to the invention.

Referring first to FIGS. 1 and 2, the tube construction there shown comprises a cathode It) in the form of a rectangular metal strip having a somewhat pointed upper end 11, said strip being attached to an electrode support wire 12 which is embedded within a moulded glass stem 13 intgeral with a button or platform 14 which also provides a mounting for the other electrodes of the structure. The wire 12 passes, in the usual way, to an external connection lead 28 extending outwardly from the tube envelope 29.

The anode 15 is in the form of an almost complete cylinder of sheet metal 16 seated at its lower end upon the upper surface of the platform 14 and closed at its opposite upper end by 21, preferably domed, closure wall 17. The anode is secured in position by interconnection with support wires 18 which are moulded in the platform 14 and at least one of which is connected to one of the external connection leads 2% of the tube.

The trigger electrode 19 is in the form of a complete or nearly complete cylinder 24 made of foraminated metal sheet disposed co-axial with the anode 15 and cathode It), the said trigger cylinder surrounding the cathode and extending from the platform 14 to a region slightly above the upper end 11 of the cathode. The upper end of the cylinder is closed by an end wall 25 also of similar foraminated metal sheet. This trigger electrode is attached and secured in position to a combined support/ connection lead 21 which is also moulded in the platform 14 of the glass stem and subsequently connected to another external connection lead 28.

To provide the necessary small dimension trigger dis charge gap between the trigger electrode 19 and the cathode 10, a part of the trigger electrode structure may conveniently be deformed slightly inwards toward the cathode, for instance, as shown at 26 in the centre of the upper end wall 25 of the cylinder. Alternatively, a part of the side wall of the trigger cylinder may be indented slightly towards the cathode, as shown in chaindotted lines at 27, to provide the required trigger gap.

A further keep-alive electrode as shown at 22 is preferably provided. This keep-alive or ionising electrode is in the form of an auxiliary cathode disposed in close-spaced relationship to the inner surface of the anode normally used in cathode construction, may be employed or alternatively'the cathode may be one coated'with emissive material. The cathode is arranged to have sufficient outer surface area to carry the'current desired 'to flow through the tube; in order to avoid the need for an inconveniently large cathode area with a central cathode as shown and described, a'r'elatively high gas-filling pres,

sure may be employed in some applications. Such gasfilling may be, for example, of neon or a mixture composed principally of neon with about 1% 'of argon,

krypton or helium. Alternatively, for some applications,

a filling consisting only or mainly of one of the inert gases or even hydrogen may be'used. The filling may be at a pressure of 200300 mm. Hg'instead of the more usual pressure or 30-50 mm. Hg for many applications although the more usual pressures in the last-mentioned range may be used where desired.

Bythe formation of a t'riggerelectrode of apertured character, it becomes relatively unimportant where the trigger gap constituted by the minimum spacing distance distance between such trigger electrode and the inner cathode happens to occur. If, instead of a foraminated .metal tube, a solid wall tube is employed as the trigger electrode and the minimum dimension breakdown path should occur at, say, the lower end of the cathode element where it is disposed deep within the confines of the trigger tube, such trigger breakdown would not be reliably effective to trigger the main discharge between the cathode and the anode. With a foraminated or like tube, the minimum spacing breakdown path is substantially equally effective wherever it happens to lie within the trigger tube.

Although in the arrangements. just described the cathode is the central electrode and the surrounding and enclosing electrode is the anode, the positions of these may be reversed with the outer cylinder forming the cathode and the centre electrode, conveniently in the form of a short wire, operating as the anode.

Various different arrangements and modifications may be made and a number of these will now be described.

Referring to FIG. 3, the anode in this modification is closed at its upper end by a mica disc 30 which may conveniently be of the usual form employed also for effecting centering and securing the electrode elements in position within the surrounding envelope 29. In this modification, the platform 14 has been replaced by a more conventional pinch type of construction as shown at 31 so that the lower end of the surrounding anode electrode is only'partially covered. The lower end of the trigger electrode 19 is preferably still closed oh however.

FIG. 4 shows yet another arrangement in which neither end of the outer cylindrical electrode, e.g. the anode 15a, is closed, the axial length of the electrode being such that it extends suificiently beyond the respective ends of the inner trigger and cathode or anode electrodes 19, 10

as to provide an effective closure thereof by virtue of extending upwardly from the upper surface of the pinch region 31 of the tube. In this embodiment, the cathode has the form of a small plate 33 disposed close to the outer surface of the trigger electrode. In this embodiment, the use of a keep-alive auxiliary cathode, as shown in FIGS. 1 and 2, is replaced by an auxiliary anode potential difierence between such anode and auxiliary cathode may be insufiicient to maintain the keep-alive discharge. By'the use of 'an auxiliary anode adjacent the main cathode, this diificulty is avoided when, as is usual, the cathode potential is constant or is likely to change comparatively little. As 'seen from the drawing, the auxiliary anode is in the form of a short wire-like member 34 positioned with its free end closely adjacent a region of the cathodeplate which is remote from the trigger electrode 19.

Another arrangement of electrodes similar to those last referred to is illustrated in FIGS. 7 and 8, wherethe cathode is again in the form of a plate 33a oriented to lie substantially radial with respect to the outer surface of the cylindrical trigger electrode 19. The auxiliary keep-alive anode, again in the form of a bent wire 34a, is arranged so that the auxiliary discharge gap-forming end thereof is close to a region of the cathode plate which is remote from the trigger electrode.

The keep-alive electrode must be so sited that the keep-alive discharge does not itself cause breakdown between the main cathode and anode electrodes but it must provide sufficient ionisation in the vicinity of the main trigger discharge gap so as to ensure the rapid build-up of a discharge in such gap.

Yet another arrangement providing an auxiliary anode type of keep-alive electrode for use with an electrode construction having a central .cathodesimilar to that described in connection with FIGS. 1 and 2 or FIG. 3 is shown in FIG. 9, where the keep-alive electrode is in the form of a wire 34b extending upwardly from the pinch region 31 outside the cylindrical anode ISa'and then bending over and entering through the open end of such anode along a path substantially co-axial with the anode cylinder and terminating at a point close to the top of the central cathode 10 within the surrounding foraminated trigger electrode cylinder 19.

Instead of using a cylindrical trigger electrode, the latter may be of elliptical or flattened cross-section as shown at 19a in FIGS. 10 and 11. Such flattened section is convenient for placing upon the upper surface of the normal flattened pinch region 31 to effect substantial closure of the lower end of the trigger electrode. In this embodiment, the cathode 10 is in the form of a small rod or fiat strip at the centre of the trigger member, 'while the anode is shown as a wire loop or hairpin-like member 35 disposed on the outside of the trigger electrode and lying in a plane normal to the cathode axis at a point substantially mid-way along the length of the trigger electrode. The keep-alive electrode, in the form of an auxiliary cathode, is constituted by a further short length of wire 36 having one end thereof disposed in closespaced relationship to an end-of the anode wire.

The apertured trigger electrode may be made of perforated metal sheet, expanded metal sheet or wire gauze. Alternatively, such electrode may be formed as a multiturn helix as shown in 19b in FIG. 12 or, as shown in FIG. 13, as a cage 19c constituted by a plurality of parallel wires extending between spaced frame posts 37 on each of the opposite sides of the latter}.

The arrangement of the apertured trigger electrode so as to surround or substantially surround one of the main cathode/anode electrodes is not essential. As shown in FIGS. 14 and 15, the trigger electrode 19d may be of approximately planar form between an anode rod 15b and a cathode plate 16 provided it is arranged so that all or substantially all of the main discharge passes through the apertures in the trigger electrode.

We claim:

l. A cold cathode gas discharge tube of the trigger type comprising a pair of main discharge cathode and anode electrodes, a trigger electrode and a keep-alive electrode located within a sealed envelope having a gaseous filling, said trigger electrode consisting of a cylinder of perforated sheet metal, a first one of said main discharge electrodes comprising a metal member located centrally within said trigger electrode cylinder and the other of said main discharge electrodes comprising a metal memberlocated outside said trigger electrode cylinder and said keep-alive electrode consisting of a further metal member located outside said trigger electrode cylinder and in close spaced relationship to the other of said main discharge electrodes, said trigger electrode cylinder being deformed inwardly towards said first one of said main discharge electrodes to provide a trigger discharge gap to said first main discharge electrode, which discharge gap is screened from the keep-alive discharge gap between said keep-alive electrode and the other of said main discharge electrodes by said trigger electrode.

2. A cold cathode gas discharge tube of the trigger type comprising a pair of main discharge electrodes, a trigger electrode and a keep-dive electrode located within a sealed envelope having a gaseous filling, said trigger electrode consisting of a perforated metal cylinder, a first one of said main discharge electrodes comprising a small area metal member located centrally within said trigger electrode cylinder and the other of said main discharge electrodes comprising a metal member located outside said trigger electrode cylinder, said keep-alive electrode consisting of a further metal member located outside said trigger electrode cylinder and in close spaced relationship to the other of said main discharge electrodes, said trigger electrode cylinder being deformed inwardly towards said first one of said main discharge electrodes to form a trigger discharge gap to said first main discharge electrode, which discharge gap is screened from the keep-alive discharge gap between said keepalive electrode and the other of said main discharge electrodes by said trigger electrode and said gaseous filling having a pressure within the range of 200300 mm. Hg.

3. A cold cathode gas discharge tube of the trigger type comprising a pair of main discharge electrodes, a trigger electrode and a keep-alive electrode located within a sealed envelope having a gaseous filling, said trigger electrode consisting of a perforated metal cylinder, a first one of said main discharge electrodes comprising a linear metal strip located coaxially within said trigger electrode cylinder and the other of said main discharge electrodes comprising an imperforate metal cylinder located outside and coaxial with said trigger electrode cylinder and said keep-alive electrode consisting of a further metal member located outside said trigger electrode cylin der and in close spaced relationship to the inner surface of said other main discharge electrode, said trigger electrode cylinder being deformed inwardly towards said first one of said main discharge electrodes to form a trigger discharge gap to said first main discharge electrode, which discharge gap is screened from the keep-alive discharge gap between said keep-alive electrode and the other of said main discharge electrodes by said trigger electrode.

4. A cold cathode gas discharge tube of the trigger type comprising a pair of main discharge electrodes, a trigger electrode and a keep-alive electrode located Within a sealed envelope having a gaseous f'dling, said trigger electrode consisting of a perforated metal cylinder, at first one of said main discharge electrodes comprising a short metal strip of small surface area located coaxially within said trigger electrode cylinder and the other of said main discharge electrodes comprising a sheet metal cylinder located outside and coaxial with said trigger electrode cylinder, said keep-alive electrode consisting of a further metal member located outside said trigger electrode cylinder and in close spaced relationship to the inner surface of said other main discharge electrode, said trigger electrode cylinder being deformed inwardly towards said first main discharge electrode to form a trigger discharge gap to said first main discharge electrode, whereby said discharge gap is screened from the keep-alive discharge gap between said keep-alive electrode and the other of said main discharge electrodes by said trigger electrode, and said gaseous filling comprising at least 99% neon at a pressure within the range of 200-300 mm. Hg.

5. A cold cathode gas discharge tube of the trigger type comprising a pair of main discharge electrodes, a trigger electrode and a keep-alive electrode located within a sealed envelope having a gaseous filling, said trigger electrode consisting of a perforated metal cylinder, a first one of said main discharge electrodes comprising a short metal rod located centrally within said trigger electrode cylinder and the other of said main discharge electrodes comprising an imperforate sheet metal member located outside and surrounding said trigger electrode cylinder and said keep-alive electrode consisting of a small metal plate located outside said trigger electrode cylinder and in close spaced relationship to the inner surface of said other main discharge electrode, means defining a trigger discharge gap between said trigger electrode cylinder and said first main discharge electrode, whereby said discharge gap is screened from the keep-alive discharge gap between said keep-alive electrode and the inner surface of said other main discharge electrode by said trigger electrode, and said gaseous filling comprising at least 99.0% neon and not more than 1% of the gases argon, krypton and helium at a pressure within the range of 200-300 mm. Hg.

6. A cold cathode gas discharge tube of the trigger type comprising of a cathode electrode, an anode electrode, a trigger electrode and a keep-alive electrode located within a sealed envelope having a gaseous filling, said envelope including a central glass stem terminating in an integral platform upon which all of the tube electrodes are mounted, said cathode consisting of a rectangular section metal strip mounted at the centre of said platform, said trigger electrode consisting of a cylinder of performated sheet metal surrounding said cathode with one end seated on said platform and its other end located above the upper end of the cathode and closed by an end Wall also of perforated sheet metal so as substantially completely to enclose said cathode, said anode consisting of a nearly complete cylinder of imperforate sheet metal surrounding said trigger electrode with one end seated on said platform and its opposite end located above the upper end of said trigger electrode cylinder and closed by an upwardly domed end wall of imperforate sheet metal and said keep-alive electrode consisting of a metal element located in close spaced relationship to the inner surface of said anode cylinder between such cylinder and the outer surface of the trigger electrode cylinder, said trigger electrode being deformed inwards towards said cathode at one point to provide a trigger discharge gap to said cathode.

7. A cold cathode gas discharge tube of the trigger type comprising of a cathode electrode, an anode electrode, a trigger electrode and a keep-alive electrode located within a sealed envelope having a gaseous filling, said envelope including a central glass stem terminating in an integral platform upon which the tube electrodes are mounted, said cathode consisting of a small area metal strip mounted at the centre of said platform, said trigger electrode consisting of a cylinder of perforated sheet metal surrounding said cathode with one end seated on said platform and its other end located above the upper end of the cathode so as effectively to enclose said cathode, said anode consisting of a nearly complete cylinder of imperforate sheet metal surrounding said trigger electrode with one end seated on said platform and its opposite end located above the upper end of said trigger electrode cylinderand said keep-alive electrode consisting of a metal plate located in close spaced relationship to the'inner surface of said anode cylinder between such cylinder and the outer surface of the triggerelectrode cylinder, said gaseous filling being at a pressure of the order of 200-300 mm. Hg.

8. A cold cathode gas discharge tube of the trigger type comprising'ofa cathodeelectrode, an anode electrode, a

trigger electrode and a keep-alive electrode located Within a sealed envelope having a gaseous filling, said envelope including a central glass stem terminating in an integral platform upon :a planar upper surface of which the tubeelectrodes are mounted, said cathode consisting of a short'rectangular section metal strip mounted at the centre of said platform perpendicular to said upper surface, said trigger electrode consisting of a cylinder of metal gauze surrounding and coaxial withsaid cathode with-one end seated on said upperplatform surface and its other end located at a level above that of the upper end of the cathode, said cylinder being closed by an upper end Wall also of metal gauze so as substantially completely to enclose said cathode, said anode consisting of a nearly complete cylinder of imperforate sheet metal surrounding said trigger electrode with one end seated on said upper platform surface and its opposite end located at a level above the upper end of said trigger elec- -trode cylinder, such opposite end being closed by an 'end wall of imperforate sheet metal and saidkeep-alive electrode consisting of a metal element located in close *spaced relationship to the inner surface of said anode cylinder between such cylinder and the outer surface of the trigger electrode cylinder, said trigger-electrode being deformed inwards towards said cathode atone point to provide a trigger discharge gap to said cathode.

-9. A cold cathode gas discharge tube of the trigger type comprising a cathode electrode, an anode electrode, a

trigger electrode and a keep-alive electrode located within'a' sealed envelope having a gaseous filling, said envelope having a central glass stem terminating at.its

upper end ina platform surface upon which all of the electrodes are mounted, said cathode consisting of'a rectilinear strip of metal disposed perpendicular to said platform surface,-said trigger electrode consisting of acylinder of perforated sheet metal disposed coaxially with said cathode strip and extending at each end beyond the respective ends of such cathode strip ,so as effectively to surround andenclose the cathode, said anode comprising a metal plate located outside saidtrigger electrode cylinder and said keep-alive electrode consisting of a metal ele- 'ment in close-spaced relationship .to said anode plate, said trigger electrode being deformed inwardly towards said cathode at one point toprovide a trigger discharge gap to said cathode.

, 10. A cold cathode gas dischargeitube of the trigger type comprising a cathodeelectrode, an anode electrode,

a triggerelectrode and a keep-alive electrode located strip so as effectively to surroundand enclose the cathode,

said anode comprising a sheet metal cylinder located outside and coaxial with said trigger electrode cylinder and having one end seated on said platform surface, and its opposite end closed by an end wall and said keep-alive electrode consisting of a metal element in close-spaced relationship'to the inner surface of said anode cylinder, said trigger electrode cylinder being deformed inwardly :towards said cathode at one point to provide a defined trigger discharge gap to saidcathode.

References Cited by theExaminer UNITED STATES PATENTS 3,023,365 2/62 Firth 313-198 DAVIS J. GALVIN, Primary'Examiner.

GEORGE N. WESTBY, Examiner. 

1. A COLD CATHODE GAS DISCHARGE TUBE OF THE TRIGGER TYPE COMPRISING A PAIR OF MAIN DISCHARGE CATHODE AND ANODE ELECTRODES, A TRIGGER ELECTRODE AND A KEEP-ALIVE ELECTRODE LOCATED WITHIN A SEALED ENVELOPE HAVING A GASEOUS FILLING, SAID TRIGGER ELECTRODE CONSISTING OF A CYLINDER OF PERFORATED SHEET METAL, A FIRST ONE OF SAID MAIN DISCHARGE ELECTRODES COMPRISING A METAL MEMBER LOCATED CENTRALLY WITHIN SAID TRIGGER ELECTRODE CYLINDER AND THE OTHER OF SAID MAIN DISCHARGE ELECTRODES COMPRISING A METAL MEMBER LOCATED OUTSIDE SAID TRIGGER ELECTRODE CYLINDER AND SAID KEEP-ALIVE ELECTRODE CONSISTING OF A FURTHER METAL MEMBER LOCATED OUTSIDE SAID TRIGGER ELECTRODE CYLINDER AND IN CLOSE SPACED RELATIONSHIP TO THE OTHER OF SAID MAIN DISCHARGE ELECTRODES, SAID TRIGGER ELECTRODE CYLINDER BEING DEFORMED INWARDLY TOWARDS SAID FIRST ONE OF SAID MAIN DISCHARGE ELECTRODES TO PROVIDE A TRIGGER DISCHARGE GAP TO SAID FIRST MAIN DISCHARGE ELECTRODE, WHICH DISCHARGE GAP IS SCREENED FROM THE KEEP-ASLIVE DISCHARGE GAP BETWEEN SAID KEEP-ALIVE ELECTRODE AND THE OTHER OF SAID MAIN DISCHARGE ELECTRODES BY SAID TRIGGER ELECTRODE. 